The same way you'd do any other roof maintenance - get back up on the roof
Not a PV expert, but ...
If you pick the right panels, then they can handle shadows - you need ones with built in diodes to bypass any cells in shadow. The series string will have reduced voltage, but a normal inverter will cope with that I think.
But you'd need a separate inverter for each series string. If you put strings in parallel, then a string with a lower output voltage (because some of it's cells are in shadow) will produce little output. So that may mean 2 or 3 standard inverters which can be wherever it's convenient - in the loft is a poor location as it gets very hot in summer and that's not good for electronics. Obviously, by the time you account for the extra cabling, switches, inverters, etc, then the cost is going to be higher.
I suspect most of the charlatans who used to sell PV (before the FITs ended and they went off to sell different snake oil) won't understand this and will only be interested in fitting an "easy" to fit system with just one inverter.